Low-power-consumption high-speed zero-current switch

ABSTRACT

A low-power-consumption high-speed zero-current switch includes a delay controller, a driving stage and a power transistor MN, wherein: an input of the delay controller is connected with an external clock CLK, an output of the delay controller is connected with an input of the driving stage, and an output of the driving stage is connected with a gate of the power transistor MN; the delay controller includes a gate signal generator, a sampling circuit and a current controller, and three of which form a negative feedback loop for stabilizing the turn-on voltage V ON  and the turn-off voltage V D  to 0, so that when the power transistor MN is turned on or off, the source-drain voltage thereof is 0. The present invention no longer uses a high-power-consumption high-speed comparator, but uses a low-power-consumption delay controller to generate turn-on and turn-off signals of the power transistor.

CROSS REFERENCE OF RELATED APPLICATION

This is a U.S. National Stage under 35 U.S.C 371 of the International Application PCT/CN2018/088421, filed May 25, 2018, which claims priority under 35 U.S.C. 119(a-d) to CN 201710381325.2, filed May 25, 2017.

BACKGROUND OF THE PRESENT INVENTION Field of Invention

The present invention relates to the field of integrated circuit design, and more particularly to a zero-current switch which mainly relates to discrete integrated circuits for automotive electronics and consumer products, and integrated circuit design in system-on-a-chip (SOC) applications such as biomedical implantable systems and consumer wireless power systems.

Description of Related Arts

Zero-current switches are widely used in various switching circuits, such as DC-DC converters, and active rectifiers. The function of the zero-current switch is that the current flowing through the switch is zero when the switch is turned on or off, thereby reducing the conduction loss of the switch and improving the reliability of the switch circuit.

The traditional zero-current switch is based on comparators. It generally includes a power MOSFET and a comparator. The power MOSFET generally includes NMOS transistors or PMOS transistors or a CMOS including NMOS transistors and PMOS transistors, and is a main path of the current. The circuit is connected or disconnected through turning on or off the power MOSFET. The comparator is configured to control the turn-on and turn-off of the power MOSFET by comparing the voltage across the power MOSFET. When the voltage across the comparator is zero, the power MOSFET is switched between turn-on and turn-off states, so that the current flowing through the power MOSFET at the time of switching is zero.

Conventional zero-current switches require higher speeds in comparators when faced with high speed requirements such as high frequency active rectifiers and high frequency DC-DC. However, high-speed comparators consume more power, so more literature is devoted to implementing low-power-consumption high-speed comparators and solving problems of high-speed comparators with low power consumption.

Literature “An efficiency-enhanced CMOS rectifier with unbalanced-biased comparators for transcutaneous-powered high-current implants,” (S. Guo and H. Lee, IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 44, NO. 6, JUNE 2009) disclosed that through a non-balanced bias current method, a fixed offset voltage VOS is introduced at an input of the comparator to achieve an advanced comparison of the comparator at a turn-off edge, thereby achieving an advanced turn-off of the zero-current switch at a lower power consumption, for further increasing the turn-off speed of the zero-current switch.

Literature “An integrated power-efficient active rectifier with offset-controlled high speed comparators for inductively-powered applications,” (H. Lee and M. Ghovanloo, IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS—I: REGULAR PAPERS, VOL. 58, NO 8. AUGUST 2011) disclosed that based on the above research, by controlling the turn-on and turn-off of the unbalanced current, two offset voltages VOS+ and VOS− are dynamically introduced at the inputs of the comparator to achieve the advanced turn-on and turn-off of the zero-current switch under certain power consumption control. The speed-up zero-current switch allows the active rectifier which includes the zero-current switch to operate at 13.56 MHz, which is within the bandwidth specified by industrial, scientific, and medical-specific frequencies (ISM) for applications in implantable systems. However, the comparator is unstable due to the two advanced offset voltages, so that multiple pulse problems are generated in the software simulation, and during the actual application, the circuit which includes the zero-current switch fails due to the oscillation.

Literature “A 13.56 MHz CMOS Active Rectifier With Switched-Offset and Compensated Biasing for Biomedical Wireless Power Transfer Systems,” (Lu Yan and Ki Wing-Hung, IEEE Trans Biomed Circuits Syst, vol. 8, pp. 334-44, June 2014) pointed out the multiple pulse and instability problems caused by the comparator using two offset voltages in the previous literature, and solved the problems by means of Switched-Offset. However, in this literature, only the double offset voltages of VOS+-VOS− in the previous literature is reduced to 0-VOS−, which reduces the probability of instability of the active rectifier, and does not fundamentally solve the stability problem caused by the double offset voltages.

Literature “Adaptive On/Off Delay-Compensated Active Rectifiers for Wireless Power Transfer Systems,” (Lin Cheng, Wing-Hung Ki, Yan Lu, Tak-Sang Yim, IEEE Journal of Solid-State Circuits, vol. 51, pp. 712-723, 2016) and literature: “A Near-Optimum 13.56 MHz CMOS Active Rectifier With Circuit-Delay Real-Time Calibrations for High-Current Biomedical Implants,” (Cheng Huang, Tom Kawajiri, Hiroki Ishikuro, IEEE Journal of Solid-State Circuits, vol. 51, pp. 1797-1809, 2016) discloses that based on the previous research, the negative feedback control technique is used to adaptively control the magnitude of the unbalanced current to control the magnitude of the offset voltage, namely, to control the compensated delay, so as to increase the speed of the zero-current switch. The conversion efficiency of the active rectifier using this zero-current switch is also increased to about 90%. For the problem of instability caused by double offset voltages, literature “Adaptive On/Off Delay-Compensated Active Rectifiers for Wireless Power Transfer Systems,” (Lin Cheng, Wing-Hung Ki, Yan Lu, Tak-Sang Yim, IEEE Journal of Solid-State Circuits, vol. 51, pp. 712-723, 2016) disclosed a one-shot circuit which utilizes the feedback set to eliminate unstable multiple pulses. However, since the one-shot circuit utilizes a feedback signal, the feedback signal competes with the input of the comparator. Once the feedback signal is later than the input of the comparator in the time domain, multiple pulses will still be generated.

Traditional zero-current switches need to increase the speed of the comparator when faced with high-speed demands. However, high-speed comparators generally generate large power consumption. The comparators based on double offset voltages used in many literatures are able to achieve faster comparisons at lower power consumption, but the double offset voltages cause the instability of the zero-current switch and affect the reliability thereof. In addition, because the offset voltage is able to provide limited delay time compensation, the comparator in the zero-current switch still consumes a relatively large amount of power.

SUMMARY OF THE PRESENT INVENTION

An object of the present invention is to provide a low-power-consumption high-speed zero-current switch for solving technical problems in existing high-speed zero-current switches.

To achieve the above object, the present invention provides a technical solution as follows.

A low-power-consumption high-speed zero-current switch comprises a delay controller, a driving stage and a power transistor MN, wherein: an input of the delay controller is connected with an external clock CLK, an output of the delay controller is connected with an input of the driving stage, and an output of the driving stage is connected with a gate of the power transistor MN;

the delay controller comprises a gate signal generator, a sampling circuit and a current controller;

the gate signal generator is configured to use the external clock CLK and two currents I_(ON) and I_(D) controlled by the current controller to generate a gate signal V_(GN) of the power transistor MN required by the zero-current switch; the sampling circuit comprises a sampling logic unit and a switched capacitor sampling unit; the sampling logic unit is configured to utilize the external clock CLK and the gate signal V_(GN) of the power transistor MN to control the switched capacitor sampling unit for sampling source-drain voltages of the zero-current switch at turn-on and turn-off moments thereof, and then transmit a sampled turn-on voltage V_(ON) and a sampled turn-off voltage V_(D) to the current controller; the current controller is configured to utilize the turn-on voltage V_(ON) and the turn-off voltage V_(D) to adaptively adjust the two currents I_(ON) and I_(D), respectively; the gate signal generator, the sampling circuit and the current controller form a negative feedback loop for stabilizing the turn-on voltage V_(ON) and the turn-off voltage V_(D) to 0, so that when the power transistor MN is turned on or off, a source-drain voltage thereof is 0.

Further, the gate signal generator comprises two cascaded current control delay line (CCDL) units, two single pulse generators and an SR (set-reset) latch, wherein: the two cascaded current control delay line (CCDL) units are respectively a first CCDL unit and a second CCDL unit; an input of the first CCDL unit is connected with CLK, a current control terminal of the first CCDL unit is connected with I_(ON), an output of the first CCDL unit is connected with an input of a second CCDL unit and an input of a first single pulse generator; a current control terminal of the second CCDL unit is connected with I_(D), an output of the second CCDL unit is connected with an input of the second single pulse generator; the first single pulse generator and the second single pulse generator respectively output two pulse signals P_(RA) and P_(FA) to two inputs of the SR latch, and an output of the SR latch outputs the gate signal V_(GN) of the power transistor MN.

Further, the first CCDL unit is controlled by I_(ON) to adjust the turn-on time of the gate signal; the second CCDL unit is controlled by I_(D) to adjust the turn-off time of the gate signal.

Further, both of the first and second single pulse generators are configured to restore the gate signal after being delayed to a short pulse, and transmit the short pulse to the SR latch for generating the required gate signal V_(GN).

Further, the current controller comprises a level shifting circuit, a first comparator CMP1, a second comparator CMP2, a logic control circuit, a current-switching integrator, a voltage to current converter and a current subtractor connected with each other in sequence, wherein: the two voltages V_(ON) and V_(D) are respectively introduced to two inputs of the level shifting circuit, and two outputs of the current subtractor respectively output the two currents I_(ON) and I_(D).

Compared with the prior art, the present invention has beneficial effects as follows. The present invention no longer uses a high-power-consumption high-speed comparator, but uses a low-power-consumption delay controller to generate turn-on and turn-off signals of the power transistor, so that the present invention is able to increase the speed of the zero-current switch at low-power-consumption. In addition, the low-power-consumption negative feedback circuit is used to control the delay of the zero-current switch, so as to ensure zero-current characteristics of the power transistor while being turned on and turned off. At the same time, due to the negative feedback characteristic of the delay controller, the robustness and the stability of the zero-current switch are greatly improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structurally schematic view of a zero-current switch provided by the present invention.

FIG. 2 is a structurally schematic view of a gate signal generator of the zero-current switch provided by the present invention.

FIG. 3 is a waveform diagram of key nodes in the gate signal generator.

FIG. 4 is a structurally schematic view of any one of the first and second CCDL units of the gate signal generator.

FIG. 5 is a waveform diagram of key nodes in any one of the first and second CCDL units.

FIG. 6 is a structurally schematic view of a current controller of the zero-current switch provided by the present invention.

FIG. 7 is a waveform diagram of key nodes in the current controller.

FIG. 8 is a topologically schematic view of a switched capacitor sampling unit of the zero-current switch provided by the present invention.

FIG. 9 is a Montecarlo simulation waveform when a source (S) of the zero-current switch is connected with ground.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a low-power-consumption high-speed zero-current switch according to a preferred embodiment of the present invention is illustrated, which is able to produce turn-on and turn-off signals of a power transistor through a delay circuit; and control a delay through a negative feedback circuit to ensure that zero-current characteristics when the power transistor is turned on and off.

FIG. 1 is a structurally schematic view of the low-power-consumption high-speed zero-current switch according to the preferred embodiment of the present invention, which comprises a delay controller, a driving stage and a power transistor MN. The power transistor MN is a main component of the low-power-consumption high-speed zero-current switch. Since the power transistor has a large gate parasitic capacitance, the delay controller is unable to be directly driven; and the driving stage is able to enhance a driving capability of signals, so that after an output signal of an active circuit passes through the driving stage, the power transistor with larger gate parasitic capacitance is driven. The delay controller generates a power-stage gate signal by means of delay control, and controls and maintains the stability of the gate signal at rising and falling times through negative feedback.

FIG. 1 is a structurally schematic view of the zero-current switch of the present invention, which comprises the delay controller, the driving stage and the power transistor MN. An input of the delay controller is connected with an external clock CLK, an output of the delay controller is connected with an input of the driving stage, and an output of the driving stage is connected with a gate of the power transistor MN.

The delay controller comprises a gate signal generator, a sampling circuit and a current controller.

The gate signal generator uses the external clock CLK and two currents I_(ON) and I_(D) controlled by the current controller to generate a gate signal V_(GN) of the power transistor MN required by the zero-current switch. The sampling circuit comprises a sampling logic unit and a switched capacitor sampling unit. The sampling logic unit utilizes the external clock CLK and the gate signal V_(GN) of the power transistor MN to control the switched capacitor sampling unit for sampling a voltage difference between a source (S) and a drain (D) of the zero-current switch at turn-on and turn-off moments thereof, and then transmits a sampled turn-on voltage V_(ON) and a sampled turn-off voltage V_(D) to the current controller. The current controller utilizes the turn-on voltage V_(ON) and the turn-off voltage V_(D) to adaptively adjust the two currents I_(ON) and I_(D), respectively. The gate signal generator, the sampling circuit and the current controller form a negative feedback loop for stabilizing the turn-on voltage V_(ON) and the turn-off voltage V_(D) to 0, so that when the power transistor MN is turned on or off, the source-drain voltage thereof is 0, thereby achieving zero-current turn-on and turn-off.

FIG. 2 is a structurally schematic view of the gate signal generator, which comprises two cascaded current control delay line (CCDL) units, two single pulse generators and an SR (set-reset) latch. An input of a first current control delay line (CCDL) unit is connected with CLK, a current control terminal of the first CCDL unit is connected with I_(ON), an output of the first CCDL unit is connected with an input of a second CCDL unit and an input of a first single pulse generator; a current control terminal of the second CCDL unit is connected with I_(D), an output of the second CCDL unit is connected with an input of the second single pulse generator; the first single pulse generator and the second single pulse generator respectively output two pulse signals P_(RA) and P_(FA) to two inputs of the SR latch, and an output of the SR latch outputs the gate signal V_(GN) of the power transistor MN.

The first CCDL unit is controlled by I_(ON) to adjust the turn-on time of the gate signal; the second CCDL unit is controlled by I_(D) to adjust the turn-off time of the gate signal, as shown in FIG. 3. Both of the first and second single pulse generators restore a delayed signal to a short pulse, and transmit the short pulse to the SR latch for generating the required gate signal V_(GN).

FIG. 4 is a structurally schematic view of any one of the first and second CCDL units of the gate signal generator. MN1 and MN2 form a current mirror. MN2 mirrors the current I_(ON) or I_(D) which passes through MN1. The first and second CCDL units control a discharge rate of a capacitor CP through controlling the current I_(ON) or I_(D). When the voltage on the capacitor drops to a certain level, the output voltage OUT flips. Different currents mean different discharge rates and different delay times, as shown in FIG. 5.

FIG. 6 is a structurally schematic view of the current controller, which comprises a level shifting circuit, a first comparator CMP1, a second comparator CMP2, a logic control circuit, a current-switching integrator, a voltage to current converter and a current subtractor connected with each other in sequence. The level shifting circuit converts a sampled voltage V_(ON) (V_(D)) into a higher voltage V_(ON) S (V_(D_S)) and provides two reference voltages V_(ON_H) and V_(ON_L) (V_(D_H) and V_(D_L)). A voltage window ranges from V_(OS−) to 0 is introduced equivalently at an input node of the level shifting circuit through V_(ON_H) and V_(ON_L). The comparators CMP1 and CMP2 respectively compare V_(ON_S) with V_(ON_H) and V_(ON_L), which is equivalent to comparing V_(ON) with V_(OS−) and 0, respectively. Moreover, the comparators CMP1 and CMP2 output digital codes for controlling turning on and turning off switches S_(inj) and S_(ext) of the current-switching integrator, thereby adjusting V_(R_ON). Through the voltage to current converter and the current subtractor, the voltage change of V_(R_ON) is able to adjust the current I_(ON). FIG. 7 is a waveform diagram of key nodes in the current controller.

The zero-current switch provided by the present invention generates the gate signal of the power transistor through the delay controlled by the current, thereby avoiding the use of a high-power-consumption comparator. Due to the successive approximation negative feedback technique, the zero-current switch based on the delay controller is able to achieve a higher switching speed at lower power consumption. The low-power-consumption high-speed zero-current switch facilitates improving performances of other circuits which adopt this switch.

In addition, the negative feedback mechanism inside the delay controller enables the active rectifier to have a good resistance to process variations, and has strong process robustness, as shown in FIG. 9. 

What is claimed is:
 1. A low-power-consumption high-speed zero-current switch, which comprises a delay controller, a driving stage and a power transistor MN, wherein: an input of the delay controller is connected with an external clock CLK, an output of the delay controller is connected with an input of the driving stage, and an output of the driving stage is connected with a gate of the power transistor MN; the delay controller comprises a gate signal generator, a sampling circuit and a current controller; the gate signal generator is configured to use the external clock CLK and two currents I_(ON) and I_(D) controlled by the current controller to generate a gate signal V_(GN) of the power transistor MN required by the zero-current switch; the sampling circuit comprises a sampling logic unit and a switched capacitor sampling unit; the sampling logic unit is configured to utilize the external clock CLK and the gate signal V_(GN) of the power transistor MN to control the switched capacitor sampling unit for sampling source-drain voltages of the zero-current switch at turn-on and turn-off moments thereof, and then transmit a sampled turn-on voltage V_(ON) and a sampled turn-off voltage V_(D) to the current controller; the current controller is configured to utilize the turn-on voltage V_(ON) and the turn-off voltage V_(D) to adaptively adjust the two currents I_(ON) and I_(D), respectively; the gate signal generator, the sampling circuit and the current controller form a negative feedback loop for stabilizing the turn-on voltage V_(ON) and the turn-off voltage V_(D) to 0, so that when the power transistor MN is turned on or off, a source-drain voltage thereof is
 0. 2. The low-power-consumption high-speed zero-current switch, as recited in claim 1, wherein: the gate signal generator comprises two cascaded current control delay line (CCDL) units, two single pulse generators and an SR (set-reset) latch; the two cascaded current control delay line (CCDL) units are respectively a first CCDL unit and a second CCDL unit; an input of the first CCDL unit is connected with CLK, a current control terminal of the first CCDL unit is connected with I_(ON), an output of the first CCDL unit is connected with an input of a second CCDL unit and an input of a first single pulse generator; a current control terminal of the second CCDL unit is connected with I_(D), an output of the second CCDL unit is connected with an input of the second single pulse generator; the first single pulse generator and the second single pulse generator respectively output two pulse signals P_(RA) and P_(FA) to two inputs of the SR latch, and an output of the SR latch outputs the gate signal V_(GN) of the power transistor MN.
 3. The low-power-consumption high-speed zero-current switch, as recited in claim 2, wherein: the first CCDL unit is controlled by I_(ON) to adjust a turn-on time of the gate signal; the second CCDL unit is controlled by I_(D) to adjust a turn-off time of the gate signal.
 4. The low-power-consumption high-speed zero-current switch, as recited in claim 3, wherein: both of the first and second single pulse generators are configured to restore the gate signal after being delayed to a short pulse, and transmit the short pulse to the SR latch for generating the required gate signal V_(GN).
 5. The low-power-consumption high-speed zero-current switch, as recited in claim 1, wherein: the current controller comprises a level shifting circuit, a first comparator CMP1, a second comparator CMP2, a logic control circuit, a current-switching integrator, a voltage to current converter and a current subtractor connected with each other in sequence, wherein: the two voltages V_(ON) and V_(D) are respectively introduced to two inputs of the level shifting circuit, and two outputs of the current subtractor respectively output the two currents I_(ON) and I_(D). 